As is well known, golf clubs are generally of two types. The "woods" which are distance clubs and the "irons." Wood golf clubs basically include a shaft having a grip portion on one end and the head attached to the other end. Most wood golf club heads are generally rounded to their rear with their face having a slight bulge therein.
The face bulge is provided to impart a spin to the ball to correct the course of the ball should the ball be stricken from an off-center portion of the face. The face bulge has a selected radius for each numbered wood club head. This radius further depends if the club head is center weighted, fore weighted or back weighted. Table 1, taken from "Golf Club Design, Fitting, Alteration and Repair" by Ralph Maltby, sets forth the face bulge radius for wood clubs numbered 1-7 depending on their center of gravity. As can be seen from Table 1, the further that the weight is moved to the back of the club, or away from the face, the more pronounced the face bulge (decreasing radius) becomes.
TABLE 1 ______________________________________ Horizontal Face Bulge Radius - Wood Clubs Club Center Fore Back No. Weighted Clubs Weighted Clubs Weighted Clubs ______________________________________ 1 10" R. 11" R. 8" or 9" R. 2. 12" R. 13" R. 10" or 11" R. 3. 12" R. 13" R. 10" or 11" R. 4. 12" R. 13" R. 10" or 11" R. 5. 14" R. 15" R. 12" or 13" R. 6. 14" R. 15" R. 12" or 13" R. 7. 16" R. 17" R. 14" or 15" R. ______________________________________
Center weighted clubs are weighted under the sole plate at the approximate middle of the club head. Drivers with an empty weight hole to reduce club head weight or with no hole, if the weight is not required, are still considered center weighted as this feature will usually only change the center of gravity in the up and down plane of the club head and not from the face to back for purposes of Table 1. Foreweighted clubs are either weighted in or behind the face insert or use heavy face inserts such as steel or brass. Also, foreweighted clubs sometimes have the weight holes under the sole plate drilled closer to the face. Backweighted clubs usually have less or no weight under the sole plate. The additional head weight is added to the back of the wood either as a brass back weight or recessed lead back weight.
Another consideration in golf club head design is the loft angle of the head. The loft angle is defined as the tilt of the face backwards from a plane normal to the sole plate. This tilt varies depending on the vertical trajectory desired for the golf ball. The loft angle increases with increasing club number so that the vertical trajectory of the ball increases as the club number increases. The standard driver loft is 11.degree. for drivers fabricated from wood.
Metal woods have recently become popular. Because of their lower center of gravity, there has been a trend towards stronger lofts (decreasing loft angles). All drivers, whether wood or metal, have a loft angle less than 14.degree.. For comparison, the standard loft angle on the one iron is 17.degree.. It is to be noted that even metal woods still require a face bulge. It would be highly desirable to provide a "wood" head with a substantially flat face to eliminate deflection of the ball along a path defined by the stroke of the club head when struck from an off center portion of the club head face.